MiJJJAJltiJ. 



i^i^ 



DEPARTMENT OF THE INTERIOR 

UNITED STATES GEOLOGICAL SURVEY 

GEORGE OTIS SMITH, DiKECTOR 

WATER-SUPPLY Paper 345— F 



THE DISCHARGE OF YUKON RIVER 
AT EAGLE, ALASKA 



BY 



E. A. PORTER AND R. W. DAVENPORT 



Contributions to the Hydrology of the United States, 1914 — P 




WASHINGTON 

GOVERNMENT PRINTING OFFICE 
1914 



_iJwi9gfapJj 



DEPARTMENT OF THE INTERIOR 
UNITED STATES GEOLOGICAL SURVEY 

GEORGE OTIS SMITH, DiRECTOE 



Water.- StnppLY Papek 345 — F 



THE DISCHARGE OF YUKON RIVER 
AT EAGLE, ALASKA 



BY 



,vl' 



V 
E. A. PORTER AND R. W. DAVENPORT 



Contributions to the Hydrology of the United States, 1914 — F 




WASHINGTON 

GOVERNMENT PRINTING OFFICE 
1914 

1/ 



^ ^ 



qJ> 



CONTENTS. 



Page. 

Location and size of the Yukon basin 67 

Climatic conditions 68 

Hydrometric data 71 

Comparison of run-off and precipitation 75 

Discharge of some large rivers in the United States, the Yukon, and the Nile. . 76 



ILLUSTRATIONS. 



Plate IV. A, Yukon River and town of Eagle, Alaska; B, Break-up of the 

Yukon May 6, 1911 70 

V. A, Yukon River after the break-up; B, Gage of the Geological Sur- 
vey on the Yukon at Eagle, Alaska 71 

Figure 3. Map of Alaska, showing boundary of Yukon River drainage basin. . . 68 

4. Rating curve for Yukon River at Eagle, Alaska 74 

II 

a OF D. 

ill 30 '914 






THE DISCHARGE OF YUKON RIVER AT EAGLE, ALASKA. 



By E. A. Porter and R. W. Davenport. 



LOCATION AND SIZE OF THE YUKON BASIN. 

Although the topographic and geographic features of the valley of 
Yukon River have been described by many writers, probably few 
people have an adequate conception of the size of the river and the 
characteristics of its flow. Brooks^ gives the Yukon fifth place 
among the large rivers in North America and estimates its catch- 
ment area at about 330,000 square miles. The approximate length 
and drainage area of some of the chief rivers of North America are 
given in Table 1 . 

Table 1. — Length and drainage area of the principal rivers of North America. 



River. 



Drainage area. 




Mississippi to head of Missouri . 

Mackenzie 

St. Lawrence 

Winnipeg and Nelson 

Yukon, with Lewes and Teshn 

Colorado and Green 

Columbia 

Ohio and Allegheny 



The Yukon heads in the northeastern part of British Columbia 
and meanders northwestward through the Yukon Territory of Canada 
to the Alaska-Canada bounda^-y near Eagle, the first Alaskan settle- 
ment which the river passes on its journey to the sea. Near the 
Arctic Circle the river bends to the southwest, and it continues in 
this general course to its entrance into Bering Sea. Its basin, as 
shown on the map, figure 3, comprises the great region lying between 
the Pacific mountain system on the south and the Rocky Mountain 
system on the north. The record of discharge of the Yukon pre- 
sented in this paper was obtained at Eagle. A view of the Yukon 
and the town of Eagle is given in Plate IV, A. The approximate 
drainage area of the Yukon at various points along its course is 
shown in Table 2. 

1 Brooks, A. II., The geography and geology of Alaska: U. S. Geol. Survey Prof. Paper 45, p. 61, 1906. 
42432°— 14 67 



68 CONTEIBUTIONS TO HYDROLOGY OF UNITED STATES, 1914. 
Table 2. — Drainage areas of Yukon River. 



Above — 



Distance 
from mouth. 



Drainage 
area. 



Dawson, Yukon Territory 

Eagle, Alaska 

Fort Yukon 

Rampart 

Mouth 



1,298 

1,208 

990 

750 





Square miles. 
115,000 
122,000 
177,000 
206,000 
330,000 




CLIMATIC CONDITIONS. 

In order to comprehend the peculiar characteristics of stream flow 
in this far northern latitude it is necessary to know something of the 
climatic conditions. The temperature at Eagle may be considered 



DISCHARGE OF YUKON EIVER AT EAGLE^ ALASKA. 



69 



tjpical of that prevailing throughout the interior region of Alaska. 
The maximum, minimum, and mean monthly temperatures at this 
place, as compiled from the Weather Bureau records for 1905 to 1912, 
are shown in Table 3. The mean annual temperature for this period 
is 23.7° F. Because of the low mean temperature to which the 
Yukon Valley is subject a very large part of its area is perpetually 
frozen to bedrock, with the exception of a shallow layer at the surface 
which can be thawed during the short, cool summers. 

Table 3. — Maxivium, minimum, and mean monthly temperature (°F.) at Eagle, Alaska, 

1905 to 1912. 





Jan. 


Feb. 


Mar. 


Apr. 


May. 


June. 


July. 


Aug. 


Sept. 


Oct. 


Nov. 


Dec. 


Maximum 

Minimum 


36 
—69 
—23.6 


45 
—56 

— 8.5 


51 
—54 
11.6 


64 
—38 
25.2 


85 
16 
47.6 


92 
24 
58.1 


91 
29 
59.6 


82 
20 
53.0 


79 
2 
41.0 


63 
—21 
26.5 


42 
-52 
2.8 


35 
—53 

— 8.4 







In general, the vegetation of the interior is sparse, as would be in- 
ferred from the condition of the ground and the shortness of the grow- 
ing season. The vegetation consists principally of moss and a thin 
growth of wild grasses. In favorable localities, however, the heat 
and sunshine of the long summer days induce rapid growth of vege- 
tation, and the wild hay and some flowering plants attain great luxu- 
riance. The forest is also generally scanty and consists chiefly of 
stunted spruces, birches, and alder brush. 

Tlie mean annual precipitation, reduced to inches of rainfall, for 
representative localities in the Yukon River basin has been compiled 
from records of the Canadian Meteorological Service and the United 
States Weathex" Bureau. Table 4 shows the stations, their location, 
the mean annual precipitation, the length of the record in months, and 
the percentage of the mean annual precipitation that occurs in the four 
principal open-season months — June, July, August, and September. 

Table 4. — Mean annv/il precipitation at stations in Yukon River basin. 



station. 



Location. 










Mean 








annual 


Duration 










precipita- 


of record 


Latitude. 


Longitude. 


tion 
(inches). 


(months). 


59 45 


133 40 


11.39 


99 


60 46 


135 00 


U.25 


64 


64 05 


139 28 


12.94 


148 


64 07 


142 20 


10.21 


61 


64 30 


142 10 


12.96 


28 


64 45 


141 10 


11.72 


171 


64 60 


147 44 


11.48 


102 


65 12 


152 00 


11.59 


148 


65 30 


150 15 


10.85 


100 



Percentage 
of annual 
precipita- 
tion faUing 
June 1 to 
Sept. 30. 



AtUn, British Columbia 

Whitehorse, Yukon Territory 

Dawson, Yukon Territory 

Kechumstuk, Alaska 

North Fork, Alaska 

Eagle, Alaska 

Fairbanks, Alaska 

Tanana, Alaska 

Rampart, Alaska 



38.4 
63.5 
44.9 
68.5 
62.0 
59.7 
55.2 
55.0 



70 CONTKIBUTIOlSrS TO HYDROLOGY OP UNITED STATES, 1914. 

These records show clearly the marked uniformity of precipitation 
throughout the Yukon River basin. The average mean annual 
precipitation at these stations is about 11,5 inches, and the data at 
hand indicate that this is a reasonable estimate for the average 
precipitation throughout the Yukon basin at elevations below 2,000 
feet. In some parts of the area increase of precipitation undoubt- 
edly accompanies an increase of altitude above 2,000 feet. Allowing 
for this increase, the mean annual precipitation of the Yukon basin 
is estimated as 13 inches. The estimate is admittedly only approxi- 
mate, but it is probably not greatly in error. 

Thus it is evident that interior Alaska is a region of small rainfall. 
Indeed, Abbe ^ has observed in regard to this region that "the range 
of precipitation is characteristic of that portion of the United States 
which lies between the Sierra Nevada and the Rocky Mountains 
north of the latitude of Salt Lake City." The meagerness of the rain- 
fall is impressed upon one who becomes acquainted with the status of 
placer mining in the interior. Large placer fields lie dormant for lack 
of water to work them, and in various localities hundreds of thou- 
sands of dollars have been spent in constructing canals that have been 
almost a total failure because of insufficient water supply. 

During the period corresponding closely to that from October to 
March, inclusive, all precipitation occurs as snow, and it accumulates 
to depths of 2 to 5 feet in the different seasons. With the warm days 
of April and May the snow commences to thaw rapidly and soon dis- 
appears from the places most exposed to the rays of the sun, but on 
the north slopes and in the deep gulches snow banks remain until far 
into the summer. The influence of the melting snow on the streams 
is large in the early summer, but as the season advances it gradually 
decreases until the run-off derived from this source is practically 
inappreciable. 

Navigation on the Yukon has so important a bearing on the com- 
merce and the f aciUty of travel in interior Alaska that it has given 
rise to a general recognition of two seasons — the "open season," 
the period duiing which the Yukon is open to navigation, and the 
" closed season," when the Yukon is either filled with floating ice or 
frozen over. Table 5 gives the dates of the break-up, or first movement 
of the ice in the spring, at Eagle, the freeze-up in the fall at the same 
locality, and the number of days the river was open, as recorded by 
the Northern Commercial Co. 

1 Brooks, A. H., and others, The geography and geology of Alaska, a siunmary of existing knowl- 
edge, with a section on climate by Cleveland Abbe, and a topographic map and a description thereof 
by H. U. Goode: U. S. Geol. Survey Prof. Paper 45, p. 156, 1906. 



U. S. GEOLOGICAL SURVEY 



WATER-SUPPLY PAPER 345 PU\TE IV 




A. YUKON RIVER AND TOWN OF EAGLE, ALASKA. 



■t.-S.'i. 



•. s 




U. BREAK-UP OF THE YUKON MAY 6, 1911. 



U. S. GEOLOGICAL SURVEY 



WATER-SUPPLY PAPER 345 PLATE V 




A. YUKON RIVER AFTER THE BREAK-UP. 




B. GAGE OF THE GEOLOGICAL SURVEY ON THE YUKON AT EAGLE, 
ALASKA. 



DISCHARGE OF YUKON EIVER AT EAGLE, ALASKA. 71 

Table 5. — Dates of the break-up and freeze-up of Yukon River at Eagle, Alaska. 



Year. 


Break- 
up. 


Freeze- 
up. 


Days 
open. 


Year. 


Break- 
up. 


Freeze- 
up. 


Days 
open. 


1898 


May 10 
May 16 
May 8 
May 12 
May 13 
May 14 
May 6 
May 9 


Nov. 8 
Nov. 2 
Nov. 13 
Nov. 1.5 
Nov. 19 
Nov. 13 
Nov. 14 
Oct. 9 


182 
170 
189 
187 
188 
183 
194 
153 


1906 


May 9 
May 3 
May 7 
May 10 
...do 


Nov. 14 
Nov. 4 
Oct. 29 
Nov. 22 
Nov. 8 
Nov. 15 
Nov. 16 


189 


1899. 


1907 


185 


1900 


1908 


175 


1901 


1909 


196 


1902 


1910 


182 


1903 


1911 


May 6 
May 3 


193 


1904 ... 


1912 


197 


1905 









The break-up of the Yukon is not only an event of great economic 
significance to the inhabitants of interior Alaska, but it presents fea- 
tures of intense dramatic interest as well. One who has not witnessed 
the break-up can hardly imagine the impressiveness of the spec- 
tacle. From bank to bank the surface of the river is a solid mass of 
huge, moving ice cakes which are constantly grinding and disinte- 
grating with an awe-inspiring exhibition of resistless force. During 
this break-up, which lasts from 7 to 12 days, the flow of the ice is 
sometimes obstructed, but finally the obstacles are overcome and the 
ice moves on, carrying away every movable thing in its path. (See 
Pis. IV, B, and V, B.) 

The freeze-up is less spectacular. With the increasing cold of 
the autumn slush ice forms in the stream and as the cold becomes 
more intense it increases in volume until finally there is sufficient to 
bridge the stream with ice. This means the termination of navigation 
on the Yukon until the following May. 

HYDROMETRIC DATA. 

At various times estimates have been made of the discharge of 
Yukon River. Engineers of the Canadian Government have made 
discharge measurements of the Yukon and its tributaries within the 
Yukon Territory.^ Brooks ^ reports an approximate measurement of 
discharge of the Yukon made by the United States Coast and Geo- 
detic Survey at a section 73 miles from the mouth. In 1909 C. E. 
Ellsworth, assistant engineer in the United States Geological Sur- 
vey, made three discharge measurements at Rampart, but no per- 
manent gaging section was there available. These results and those 
of other investigations of the surface water supply of the Yukon- 
Tanana region, from 1907 to 1912, have been compiled for publica- 
tion.^ 

Not until 1911 was it practicable to maintain a regular gaging 
station on Yukon River. . This station was established at Eagle in 

' Ogilvie, William, The Klondike official guide, p. 56, Buffalo, 1898. Canada Commission of Conservation, 
Water powers of Canada, p. 288, Ottawa, 1911. 

2 Brooks, A. H., The geography and geology of Alaska: U. S. Geol. Survey Prof. Paper 45, p. 65, 1906. 

3 Ellsworth, C. E., and Davenport, R. W., U. S. Qeol. Survey Water-Supply Paper 342 (in press). 



72 OOlsTTRIBUTIONS TO HYDEOLOGY OF UNITED STATES, 1914. 

May, 1911, by C. E. Ellsworth and E. A. Porter. During 1911 it was 
maintained under the personal supervision of E. A. Porter, and dur- 
ing 1912 under that of R. W. Davenport. Observations of daily gage 
heights were made by W. P. Thrall, agent of the Northern Commercial 
Co., at Eagle, during the open seasons of 1911, 1912, and a part of 1913. 

The long, easily sloping gravel banks of the Yukon and the destruc- 
tive action of ice to which they are subject make the selection of a 
permanent site for a gage a difficult problem. At Eagle, however, 
an admirable site was found on the high bluff that juts into the 
stream just below the town. On the vertical face of this bluff a 
white strip 3 feet wide and about 18 feet high was painted, as shown 
in Plate V, B. This white strip was graduated in black paint at inter- 
vals of a quarter of a foot and the even feet were marked with num- 
bers large enough to be read by a telescope from the hotel piazza at 
Eagle, about half a mile distant. The gage was installed before the 
break-up of May 6, 1911, when the river was at a very low stage. The 
observer read the gage to one-eighth of a foot. A study of the rating 
curve shows that at medium stages the ratio of increase of discharge 
to increase of gage height is such that reading the gage to one-eighth 
of a foot does not introduce into the discharge an error of more than 
1 per cent. This amount is well within the limits of accuracy ordi- 
narily required for observations of gage heights. 

The only feasible method for making open-channel discharge 
measurements of the Yukon is by floats. About 2 miles above Eagle 
a stretch of channel was selected which is straight for about 1,000 
feet and through which its cross section was believed to be practically 
uniform. The river at this point is about 1,600 feet wide. About 
midlength of the proposed run for the floats the cross section was 
determined by cutting holes through the ice at intervals of 50 feet 
and making soundings at each hole. The exposed section was deter- 
mined by levels and, with the section obtained by soundings, was 
referred to a permanent benchmark. 

On April 22, 1911, the vertical velocity of the stream at each ice hole 
was determined by a Price cxu-rent meter and the discharge was com- 
puted as 10,100 second-feet. This is considered to be the minimum 
discharge of the Yukon, at Eagle for 1911, and it will probably repre- 
sent very closely the minimum from year to year. 

Dm'ing May, 1911, seven discharge measurements were made by 
means of ice floats. About May 1 the Yukon began to rise rapidly 
from the melting snows, and by May 6 the river had become so high 
that the ice covering the river could no longer remain intact. On 
this date the "break-up " began and it continued for about ten days. 
Toward the end of this period the floating ice gradually became but 
thinly spotted across the surface of the river, while the banks on both 



DISCHARGE OF YUKON RIVER AT EAGLE, ALASKA, 73 

sides were piled high with large blocks of ice varying in thickness 
from 3 to 8 feet. The condition of the river at the time when these 
discharge measurements were made is shown in Plate V, A. The in- 
struments used were a transit and a stop watch. The passage of ice 
cakes was timed over a run of 500 feet and their location was deter- 
mined by triangulation. Two men selected a cake as it crossed the 
upper range and while one man followed it with the transit telescope, 
the other went down to the lower range and when the float crossed 
signaled the transitman and noted the time. 

In 1912 three measurements were made, two when driftwood was 
coming down the river in sufficient quantities to serve as floats and 
one by means of bottle floats. For the bottle floats beer bottles were 
weighted with sand and were marked with flags stuck in the necks. 
White flags were found to be best adapted to be seen at a distance 
over the water surface. These floats were dropped by a boatman in a 
rowboat at intervals of about 75 feet across the stream above the 
upper range line. 

In 1912 observations were made to determine the coefficient to be 
applied to the surface velocities to reduce to the mean velocity. In 
a stream so large and swift as the Yukon the determination of the ver- 
tical velocity curve presents some interesting problems. The most 
serious of these problems was to find a method of holding one position 
in the stream long enough to measure velocities at the desired depths- 
The method which proved successful was by using a rowboat with 
a sack of rocks as an anchor. A rope was fastened to the sack of 
rocks, then it was secured to the bow of the boat and carefully ar- 
ranged in a coU. The boat was hauled far above the measuring sec- 
tion and. when all was ready it was energeticaUy rowed out into the 
channel, the swift current carrying it rapidly downstream in the 
meantime. When the desired position in the channel was reached 
the sack of rocks was thrown over, and as soon as it held the boat the 
Telocities were determined at the required depths with the current 
meter. It was found necessary to use about 200 pounds of rocks to 
furnish sufficient anchorage. When the observations at one point 
were completed the rope was cut, the boat pulled to shore, and the 
operation repeated. The results of these observations indicated a 
coefficient of 0.92, which has been used for the reduction of all dis- 
charge measurements, the results of which are tabulated in Table 6 
and shown in figure 4, With one exception these measurements 
plot within 3 per cent of the mean curve of relation between gage 
heights and discharge. The measiu-ement of May 19, 1911, plots 15 
per cent greater than this curve, probably because of certain abnor- 
mal conditions of ice flow at the time of the measurement. It has 
been disregarded in the preparation of the rating curve. 



74 CONTEIBUTIOlSrS TO HYDROLOGY OF UNITED STATES, 1914. 
Table 6. — Discharge measurements on Yukon River at Eagle, Alasha, 1911 and 1912. 



Date. 



Gage 
height. 



Discharge. 



Reference 
number 

on 
figure 4. 



Apr. 22. 
May 9. 

10. 

16. 

19. 

20. 

21. 

22. 



May 21.. 
July 29.. 
Sept. 14. 



1911. 



Feet. 



1912. 



2.90 
3.10 
2.40 
7.50 
10.10 
11.25 
11.90 



3.45 
9.65 
-2.00 



Second-feet, 
a 10, 100 
125, 000 
125, 000 
121,000 
216, 000 
235,000 
238,000 
253,000 



127, 000 
223,000 
68,200 



o- Discharge measured through ice. 



I- 
ui 8 



t4 















• 








7 


^^ 




















60 














R 




^ 


'" 


A-° 














2- 


^ 
















^ 


y^ 















































40,000 W,000 120,000 160,000 200,000' 240,000 

Figure 4. — Rating curve for Yukon River at Eagle, Alaska. 

The maximum discharge measurement was made May 22, 1911, 
when the discharge was 253,000 second-feet. The width of the 
water surface at the measuring section was 1,645 feet, and the greatest 
depth was 28.7 feet. The surface velocity at this point of greatest 
depth was 9.52 feet per second and the mean surface velocity for the 
section was 8.55 feet per second, which corresponds to a current of 5.8 
miles an hour. From Eagle to Whitehorse the grade of the river 
is higher than below Eagle, and steamboats can make but slow 
progress upstream. With the continual shifting of the channel near 
Circle and the Yukon Flats and the swift currents to be overcome in 
the upper section of the river, navigation on the Yukon is not easy. 

Table 7 shows the mean monthly discharge, run-off in second-feet 
per square mile, and run-off in inches on the drainage area for 1911, 
1912, and 1913. The gage-height record was kept for 145 days in 
1911, for 155 days in 1912, and for 80 days in 1913. The monthly 
means for the remaining parts of this three-year period are obtained 



raSCHAEGE OF YUKOlSr RIVER AT EAGLE, ALASKA. 



75 



from estimates based on data of precipitation, a personal knowledge of 
the conditions, and such miscellaneous measurements of discharge 
as have been made in winter. 

Over two-thirds of the estimated total run-off of this period was 
determined from the gage-height record, and the monthly mean 
should have a probable error not exceeding 10 per cent. The margin 
of error in the estimated portion of the run-off may therefore be 
fairly large without increasing the probable error of the total very 
appreciably. It seems reasonable to set the probable error of the 
mean results for the three years as shown in Table 7 at 10 per cent. 

Table 7. — Monthly discharge of Yukon River at Eagle, Alaska, 1911, 1912, and 1913. 



Month. 



January . . 
February. 

March 

April 



June 

July. 

August 

iBeptember. 
October... 
November. 
December. 



The year.. 
Mean for 3 years . 



Discharge in second-feet. 



1911 



21, 000 

15, 000 

11,000 

12, 000 

156,000 

184, 000 

178,000 

139, 000 

106, 000 

60, 000 

37, 000 

28, 000 



78, 900 



21, 
15, 
11, 

12, 
125, 
160, 
147, 
127, 
73, 
51, 
37, 
28, 



67, 300 
73, 200 



21, 000 

15,000 

11,000 

12, 000 

117, 000 

199, 000 

164, 000 

133, 000 

90, 000 

55, 000 

37, 000 

28, 000 



73, 500 



Second-feet per square Run-ofl (depth in inches 
mile. on drainage area). 



1911 



0.172 
.123 
.090 
.098 
1.28 
1.51 
1.46 
1.14 
.869 
.492 
.303 
.230 



1912 



0.172 
.123 
.090 
.098 
.959 
1.63 
1.34 
1.09 
.738 
.451 
.303 
.230 



1911 



0.20 
.13 
.10 
.11 

1.48 

1.68 

1.68 

1.31 

.97 

.57 

.34 

.27 



8.84 



1912 



0.20 

.13 

.10 

.11 

1.18 

1.47 

1.38 

1.20 

.67 

.48 

.34 

.27 



7.53 
8.19 



0.20 

.13 

.10 

.11 

1.11 

1.82 

1.54 

1.26 

.82 

.50 

.34 

.27 



8.20 



COMPARISON OF RUN-OFF AND PRECIPITATION. 

Although the data are insufficient for a comparison of run-off and 
precipitation that would afford conclusive results, they suffice to em- 
phasize certain interesting characteristics of run-off in the Yukon 
drainage basin. 

Table 8 shows the mean annual precipitation at stations in the 
drainage area above Eagle and other stations in the Yukon Valley 
for the period from November 1, 1910, to October 31, 1913, and its 
percentage of the mean record at the respective stations. This table 
shows a well-defined tendency for the precipitation of this period to 
be below the normal. Assuming that the mean of the percentages 
represents the prevaihng condition throughout the basin and con- 
sidering 13 inches as the normal rainfall in the same area, we find that 
the mean annual rainfall in the basin for the three water-years con- 
sidered is approximately 12 inches. The same process of reasoning 
leads to the befief that the computed mean discharge of the Yukon 
at Eagle is also probably a little below the normal. The mean annual 
run-off in depth in inches on the drainage area is given in Table 7 
as 8.19. Thus it appears that the run-off is approximately 65 per 



76 CONTEIBUTIONS TO HYDROLOGY OF UNITED STATES, 1914. 



cent of the precipitation for the three water-years from November 1, 
1910, to October 31, 1913. 



Table 8. — Annual precipitation in inches at stations in Yukon River basin, Nov. 1, 1910, 

to Oct. .31, 1913. 



Station. 



Nov. 1, 


Nov. 1, 


Nov. 1, 




Mean an- 
nual pre- 
cipitation 

from 
Table 4. 


1910, to 


1911, to 


1912, to 


Mean for 


Oct. 31, 


Oct. 31, 


Oct. 31, 


period. 


1911. 


1912. 


1913. 




10.82 


8.77 


10.62 


10.07 


11.. 39 


15.33 


9.80 


a 9. 52 


11.32 


12.94 


12.90 


10.94 


8.63 


10.82 


11.72 


11.73 


10.52 


10.13 


10.79 


11.48 


12.30 


12.75 


10.19 


12.08 


11.59 


8. 62 


11.12 


8.18 


9.31 


10.85 



Per cent 
of mean 
annual 
precipita- 
tion. 



Atlin, British Columbia. . . 
Dawson, Yukon Territory , 

Eagle, Alaska 

Fail-banks, Alaska , 

Tanana, Alaska 

Bampart, Alaska 



92 
94 
104 
86 



o Records for March, April, and June lacking, 
the respective months was substituted. 



To obtain the result the mean monthly precipitation for 



Comparing this result with that for various drainage basins through- 
out the United States, one is apt to question the accuracy of so high 
a percentage of run-off. The drainage area of the Yukon presents 
conditions decidedly different from those in most of the river basins 
of the United States. Except for the shallow layer at the surface, 
which can be thawed during the short, cool summer, practically the 
whole area above Eagle remains perpetually frozen to bedrock. Con- 
sequently when the thawed earth has become saturated the rainfall 
can only seek its way to the nearest stream. The topography and 
climate of the region are unfavorable for great losses by evaporation, 
the grades of the streams and slopes of the valleys are comparatively 
large, and the lake area is small. The growing period for vegetation 
is short and is too cool for a luxuriant growth, and losses due to 
vegetation are relatively small. Therefore a run-off of 65 per cent 
of the rainfall for interior Alaska is believed to at least approximate 
the true ratio. 

On consideration of the small run-off and the intense cold of the 
winter season in interior Alaska it is evident that surface mining and 
power development of any large amount must cease for a large por- 
tion of the year. The records show that the greater part of the pre- 
cipitation occurs during the open season and that much the greater 
part of the run-off occurs during the same period. The topography, 
chmate, and vegetation of the area are such that the ratio of run-off 
to precipitation is abnormally large. 

DISCHARGE OF SOME LARGE RIVERS IN THE UNITED 
STATES, THE YUKON, AND THE NILE. 

An interesting table has been compiled by G. C. Stevens, of the 
United States Geological Survey, showing the discharge of some of 
the large rivers in the United States, of the Yukon, and of the Nile 
in Egypt. The sources of the various records are given in footnotes. 



DISCHARGE OF YUKON RIVER AT EAGLE^ ALASKA. 



77 



Table 9. — Discharge of some large rivers in the United States and of the Yukon and the 

Nile. 



River. 


Point. 


Drainage 
area. 


Discharge in second-feet. 


Maximum. 


Minimum. 


Mean. 




Mouth 


Sq. miles. 

1,238,000 
171,500 
202,000 
527,000 
26, 800 
248,000 
225,000 
237,000 
122,000 
383,300 

1,262,000 


1,800,000 
360,000 

1,400,000 

600, 000 

353,000 

35, 600 

150,000 

1,390,000 
254,000 
330,000 
353,000 


125,000 
25,000 
21,000 
6,000 
2,200 
650 
2,700 
48,500 
10,100 
185,000 
14, 500 


695,000 
127,000 


Do b 


Grafton, 111 


Ohio 6 


Paducah, Ky 


300,000 

100,000 

38,800 

7,100 




St. Charles, Mo 




McCall Ferry Pa 




Brownsville^ ^ex 




Yuma, Ariz . . . 


23 300 




The Dalles, Greg 


235,000 
73, 200 


Yukon/ 


Eagle, Alaslsa 




Ogdensburg, N. Y 

Assouan, Egypt 


252 000 


Nile A 


116,000 







a Drainage area and mean discharge from IT. S. Geol. Survey Water-Supply Paper 234; maximum and 
minimum values are conclusions from a paper by WUUam Starling, The discharge of the Mississippi Riveri 
Am. See. CivU Eng. Trans., vol. 34, November, 1895. 

b From reports United States Army Engineers. 

c From United States Geological Survey records. 

d From measurements by International Boundary Commission, Mexican section, published by United 
States Geological Survey. 

e From United States Geological Survey records. Drainage area at mouth is 259,000 square miles. 

/ From United States Geological Survey records. Drainage area at mouth is 330,000 square miles. 

g From a report of E . S. Wheeler, assistant engineer, United States Army. Chief Eng. Rept., 1903, part 4. 

k Peale, Sidney, The binding of the Nile and the new Sudan. 



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